How to compress and scale down an NSImage? - objective-c

Question

This is my compress code
NSBitmapImageRep* tmpRep = [[_image representations] objectAtIndex:0];
[tmpRep setPixelsWide:512];
[tmpRep setPixelsHigh:512];
[tmpRep setSize:NSMakeSize(SmallThumbnailWidth, SmallThumbnailHeight)];
NSDictionary* imageProps = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:0.3] forKey:NSImageCompressionFactor];
NSData* outputImageData = [tmpRep
representationUsingType:NSJPEGFileType properties:imageProps];
NSString* imageFilePath = [NSString stringWithFormat:#"%#/thumbnail.jpg",imagePath];
[outputImageData writeToFile:imageFilePath atomically:YES];
The original image size is 960*960.I want to compress the original image into 512*512.But the output Image's size is 960*960 when I check it in finder and the location size which compares with the original has really been compressed.Any one could tell me why ? thank you

Answer 1

Try this one:
This will reduce the saving size in kbs:
-(NSImage *)imageCompressedByFactor:(float)factor{
NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithData:[self TIFFRepresentation]];
NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:factor] forKey:NSImageCompressionFactor];
NSData *compressedData = [imageRep representationUsingType:NSJPEGFileType properties:options];
return [[NSImage alloc] initWithData:compressedData];
}
This will reduce the file size in pixels :
Copied from here
#implementation NSImage (ProportionalScaling)
- (NSImage*)imageByScalingProportionallyToSize:(NSSize)targetSize{
NSImage* sourceImage = self;
NSImage* newImage = nil;
if ([sourceImage isValid]){
NSSize imageSize = [sourceImage size];
float width = imageSize.width;
float height = imageSize.height;
float targetWidth = targetSize.width;
float targetHeight = targetSize.height;
float scaleFactor = 0.0;
float scaledWidth = targetWidth;
float scaledHeight = targetHeight;
NSPoint thumbnailPoint = NSZeroPoint;
if ( NSEqualSizes( imageSize, targetSize ) == NO )
{
float widthFactor = targetWidth / width;
float heightFactor = targetHeight / height;
if ( widthFactor < heightFactor )
scaleFactor = widthFactor;
else
scaleFactor = heightFactor;
scaledWidth = width * scaleFactor;
scaledHeight = height * scaleFactor;
if ( widthFactor < heightFactor )
thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
else if ( widthFactor > heightFactor )
thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
}
newImage = [[NSImage alloc] initWithSize:targetSize];
[newImage lockFocus];
NSRect thumbnailRect;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width = scaledWidth;
thumbnailRect.size.height = scaledHeight;
[sourceImage drawInRect: thumbnailRect
fromRect: NSZeroRect
operation: NSCompositeSourceOver
fraction: 1.0];
[newImage unlockFocus];
}
return [newImage autorelease];
}
#end

Answer 2

Create a category method like so, in order to incrementally compress the image till you meet the desired file size:
- (NSImage*) compressUnderMegaBytes:(CGFloat)megabytes {
CGFloat compressionRatio = 1.0;
NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithData:[self TIFFRepresentation]];
NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:compressionRatio] forKey:NSImageCompressionFactor];
NSData *compressedData = [imageRep representationUsingType:NSJPEGFileType properties:options];
while ([compressedData length]>(megabytes*1024*1024)) {
#autoreleasepool {
compressionRatio = compressionRatio * 0.9;
options = [NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:compressionRatio] forKey:NSImageCompressionFactor];
compressedData = [imageRep representationUsingType:NSJPEGFileType properties:options];
// Safety check, 0.4 is a reasonable compression size, anything below will become blurry
if (compressionRatio <= 0.4) {
break;
}
}
}
return [[NSImage alloc] initWithData: compressedData];
}
You can then use it like this:
NSImage *compressedImage = [myImage compressUnderMegaBytes: 0.5];

Answer 3

level from 0.0 to 1.0
func getImageQualityWithLevel(image: NSImage, level: CGFloat) -> NSImage {
let _image = image
var newRect: NSRect = NSMakeRect(0, 0, _image.size.width, _image.size.height)
let imageSizeH: CGFloat = _image.size.height * level
let imageSizeW: CGFloat = _image.size.width * level
var newImage = NSImage(size: NSMakeSize(imageSizeW, imageSizeH))
newImage.lockFocus()
NSGraphicsContext.currentContext()?.imageInterpolation = NSImageInterpolation.Low
_image.drawInRect(NSMakeRect(0, 0, imageSizeW, imageSizeH), fromRect: newRect, operation: NSCompositingOperation.CompositeSourceOver, fraction: 1)
newImage.unlockFocus()
return newImage
}